This invention relates to a magnetoresistance effect (MR) element, its manufacturing method, and its use as a magnetic recording element or a magnetic memory. More particularly, the invention relates to a magnetoresistance effect element having magnetic nanocontacts that exhibit high magnetoresistance ratios, its manufacturing method, and its use as a magnetic reproducing element or a magnetic memory.
Since the discovery that a giant magnetoresistance effect occurs when a current is supplied to flow in parallel with the major plane of a multi-layered structure, efforts have been made to find systems having still larger magnetoresistance ratios. Thus, ferromagnetic tunnel junction elements and CPP (current perpendicular to plane) type MR elements in which electric current flows vertically in a multi-layered structure have been developed and suggested for use as magnetic sensors and reproducing elements for magnetic recording.
In the technical field of magnetic recording, enhancement of the recording density inevitably requires miniaturization of the recording bit, and this makes it more and more difficult to ensure sufficient signal intensity. Accordingly, materials exhibiting an even more sensitive magnetoresistance effect are in demanded, and the importance of systems having large magnetoresistance ratios, as referred to above, is greater and greater.
Recently, “magnetic nanocontacts” by tip-to-tip abutment of two nickel (Ni) needles and nanocontacts by contact of two magnetite elements have been reported as elements exhibiting 100% or higher magnetoresistive effects, see (1) Garcia, M. Munoz and Y.-W. Zhao, Physical Review Letters, vol.82, p2923(1999) and (2) J. J. Versluijs, M. A. Bari and J. W. D. Coery, Physical Review Letters, vol.87, p26601-1 (2001), respectively. These nanocontacts certainly exhibit large magnetoresistive changes. In both proposals, however, the magnetic nanocontacts are made by bringing two needle-shaped or triangular-shaped ferromagnetic elements into tip-to-tip contact.
More recently, magnetic nanocontacts have been formed by arranging two thin nickel wires in a “T”-configuration and by growing a micro column at the connecting point thereof by electroplating technique, see (3) N. Garcia et. al., Appl. Phys. Lett., vol.80, p1785 (2002) and (4) H. D. Chopra and S. Z. Hua, Phys. Rev. B, vol.66, p.20403-1 (2002).
These magnetic nanocontacts also exhibit a large mangetoresistance change, however, the structure of these magnetic nanocontacts makes it almost impossible to realize a practical magnetoresistance effect element.
Another group has reported a magnetic nanocontact which was formed by growing a cluster of nickel using an electroplating technique in a pinthrough hole made on an alumina layer, see (5) M. Munoz, G. G. Qian, N. Karar, H. Cheng, I. G. Saveliev, N. Garcia, T. P. Moffat, P. J. Chen, L. Gan, and W. F. Egelhoff, Jr., Appl. Phys. Lett., vol. 79, p.2946, (2001).
However, it is difficult to control the magnetic domain structure and the configuration of the point contact, therefore, the resulting magnetoresistance ratio is as small as 14% or even smaller.
Magnetic nanocontacts have a potential to exhibit a large magnetoresistance ratio, however, in order to ensure a large magnetoresistive effect therewith, the structures proposed by the above-noted articles include placing two needle-shaped ferromagnetic elements in tip-to-tip abutment or growing a micro column between two wires by an electroplating technique, and this and other requirements make it difficult to accurately control the contact portions in the manufacturing process. Taking into account of the application of such magnetic nanocontacts to magnetic heads or solid magnetic memory devices, however, it is necessary to develop a structure for nanocontacts that is suitable for mass production under reasonable control, as well as the manufacturing method to achieve such a structure. Additionally, to detect the difference in magnetization directions on opposite sides of a nanocontact, control of magnetic domains of both magnetic electrodes is important. Therefore, in order to realize a practical magnetoresistance effect element, it is essential to develop a structure where the control of the magnetic domains of the both magnetic electrodes is quite easy.